Wow, excellent piece. It reminds me a bit of James Horner's work in A Beautiful Mind.
Excuse the very short post, but I've just listened to it 3 straight times and wanted to quickly post how much I'm enjoying it. :)
Oh, and definitely go for it (composing film scores). I obviously don't know if you'd be able to consistently turn out pieces like this, but c'mon, you're only 15, and you seem to be far along already. I look forward to hearing your future work.